Land Division Fact Sheet 3 Water Sensitive Urban Design

Land Division Fact Sheet 3 Water Sensitive Urban Design

3 sustainable residential subdivision design fact sheet seriesThe District Council of Mount Barkerfact sheet threeWater Sensitive UrbanDesign (WSUD)This is the third in a series of fact sheetsproduced by the District Council of MountBarker on Sustainable ResidentialSubdivision Design. Council’sDevelopment Plan identifies a number ofareas within and adjacent to existingtownships that are intended for residentialdevelopment. A number of policies withinthe Development Plan require thatresidential development, includingresidential subdivisions, satisfy a range ofsustainability objectives and principles.This is one of five fact sheets, which coverthe following topics:• Site Analysis• Energy Efficiency Water Sensitive Urban Design(WSUD)• Biodiversity, Open Space and Buffers• Sustainable TransportWhat do we mean by WaterSensitive Urban Design(WSUD)?Water Sensitive Urban Design (WSUD) isan holistic approach to the planning anddesign of urban development that aims tominimise negative impacts on the naturalwater cycle and protect the health ofaquatic systems. It promotes theintegration of stormwater, water supplyand sewage management at thedevelopment stage.The general objectives for WSUD are to:• maintain the natural (i.e. predevelopment)hydrologic regime• maintain and, where possible,enhance the water quality of surfaceand ground water• encourage water conservation, and• maintain and enhance water-relatedenvironmental, recreational andcultural values and opportunities.Why do we need WSUD?Urban development usually results in amore intensive use of land, an increasedpopulation and an increase in imperviousarea. These changes can:• increase surface runoff• increase pollutant loads and erosiveforces on receiving watercourses• place capacity pressure ondownstream infrastructure• adversely effect flood levels• reduce soil moisture, water rechargeand stream base flows• increase sewage flows, and• increase water demand.WSUD represents a shift in the way urbandevelopment is conceived, planned,designed and built. Rather than usingtraditional approaches to impose a singleform of urban development across alllocations, WSUD considers ways in whichurban infrastructure can be integratedwithin the natural features of a site. Italso seeks to optimise the use of water asa resource.WSUD can help counteract many of thepotential adverse impacts of urbandevelopment on the natural water cycle.By incorporating water sensitive measuresin the design and planning of landdivisions it is possible to:• reduce flood risk in urban areas• prevent erosion of waterways, slopesand banks• improve water quality in streams andgroundwater• make more efficient use of waterresources• reduce the cost of providing andmaintaining water, stormwater andwastewater infrastructure• protect and restore aquatic andriparian ecosystems and habitats, andFact Sheet Three - Water Sensitive Urban Design Page 1 of 9

3 sustainable residential subdivision design fact sheet seriesThe District Council of Mount Barker• protect the scenic, landscape andrecreational values of streams andtherefore improve amenity and thevalue of the development.The key principles of WSUD are outlined inTable 1 at the end of this Fact Sheet,along with examples of how they can beapplied in an urban development. Manyopportunities exist for WSUD elements toaddress more than one principle.Maximising the multiple benefits createdby innovative design is an essential aspectof good WSUD practice. The approach isable to add value while minimisingdevelopment costs.How does WSUD differ fromtraditional approaches?Traditional water supply, stormwater andwastewater practices have been largelybased on centralised collection,conveyance and treatment of water flows.Whilst highly effective in some areas,these methods can also have majordrawbacks, such as inefficient use ofwater resources, environmentaldegradation, flooding and risinginfrastructure costs. Conveyance does notsolve the problem but merely transfers itto the other end of the pipe and ultimatelydisturbs the local water balance.Steps in the land divisionprocessA number of steps have been identifiedwhich should be followed when submittinga development application to Council for aland division development. Followingthese steps will assist in reducing thepotential for delays in the approvalprocess.Consider relevant provisions of theDevelopment Plan and LegislationThe relevant provisions of theDevelopment Plan need to be consideredfrom the outset to ensure that Councilrequirements are met. Specialconsideration should be given to theConcept Plans for land division containedin the Development Plan. Relevant Stateand Federal Legislation must also beconsidered (see Table 1).Review the physical properties of thesite and identify specific constraintsWSUD is applicable on all sites but thedegree of application will vary according tothe site opportunities and constraints. Asite analysis will need to be conducted asdetailed in Fact Sheet One - SiteAnalysis.Included in this site analysis will be anidentification of the potential impacts ofthe development on the existingenvironment.Identify WSUD measures which areconsidered suitable for inclusion inthe development (land division scaleand allotment scale)This stage will involve matching the likelyimpacts with the most appropriate WSUDdesign elements to achieve a sustainablebalance between development and theenvironment. Depending on localconditions, suitable measures may includeswales, sand / gravel filters, landscapedfilter strips and detention basins. Thesecan be combined to form an integratedsystem, and an improved landscape.For example, streets can be designed toincorporate a variety of stormwaterdetention and treatment measures. Streetlayout should respond to site topography(where possible), with streets alignedclose to contours to eliminate the need forlarge-scale earth moving, whilst reducingstormwater velocities.Recreational areas may also incorporatewater features that have a multi-purposeof stormwater detention and treatment.However, it should be noted that areasthat are intended to be used for thepermanent retention of water withinrecreational areas cannot be considered aspart of the required open spacecontribution (see Principle 20, 46e, and166b of District Council of Mount BarkerDevelopment Plan).It is important to be aware that WSUDcannot be considered on its own - theelements in the other four fact sheets ofthis series need to be taken into accountand conflicts between the elements mayarise. Therefore, a compromise betweenthe elements may need to be made.Fact Sheet Three - Water Sensitive Urban Design Page 2 of 9

3 sustainable residential subdivision design fact sheet seriesThe District Council of Mount BarkerSome of the more common components ofWSUD are summarised in Table 1 anddescribed below.Consult with CouncilBefore going to the expense of designinga site layout, it is recommended that thefindings of the previous steps of theprocess be discussed with the relevantofficer of Council to ensure that theconcept is progressing along the right pathand that the requirements of theDevelopment Plan can be met. Councilwill also be able to suggest whetherconsultation with any governmentagencies is appropriate or required (e.g.the Environment Protection Authority orthe Natural Resources ManagementBoard).On-going maintenance issues with anypotential WSUD elements will also need tobe considered and discussed with Councilat this stage of the process.Develop an appropriate layoutBased on the findings of the previoussteps, an appropriate site layout will needto be prepared which takes into accountWSUD elements as well as solarorientation, sustainable transport andbiodiversity issues.Analysis of pre-development andpost-development flows (volume,quality and frequency) from the siteCouncil require on-site detention to ensurerunoff from the development does notexceed pre-development rates. This is notonly to ensure flooding is not exacerbateddownstream, but also to maintain naturalwater regimes for valuable wetlands andcreeks. This may require additional onsitestorage of stormwater as well as floodconveyance and the application of otherwater sensitive planning and managementpractices. However, if the applicant candemonstrate that the existing catchmenthas an adequate drainage system,detention may not be required or could beminimised. In order to establish thisrequirement, the applicant will need toprovide a study prepared by a suitablyqualified civil engineer which analyses thewhole catchment and demonstrates that:• the capacity of the existing drainagesystem is adequate for postdevelopmentrunoff and allows forincreased development of other siteswithin the catchment• there is no increase in the incidence offlooding downstream, and• there is no impact on downstreamwater quality or an increase inerosion.(Please note that the Council is currentlyestablishing standards for stormwatermanagement which will define the stormevent requiring on-site detention.)Stormwater runoff from rare and intensestorm events can pose serious risks to lifeand property. It is essential that thedesign of overland flow paths, on-sitedetention storage and other stormwatermanagement measures meet relevantsafety criteria for pedestrians, vehicles andproperty damage.Detention and retention of water on thesite may also be required to meet waterquality targets that may be set by Council,the Environment Protection Authority orthe Natural Resources Management Board.Approvals processAn application for land division must belodged with the Development AssessmentCommission. An application may belodged in two stages by initially applyingfor Provisional Development Plan Consentonly. A further application can then bemade (within 12 months) for completeDevelopment Approval. The application isforwarded to the local council and to anygovernment agencies which may need tobe consulted. The extent of theconsultation depends on the location,nature and magnitude of the proposal.See Guide for Applicants – Land DivisionGuide( designOnce the various elements have beenidentified and the development layoutrefined, detailed sizing of each elementcan proceed (either before or afterProvisional Development Plan Consent hasbeen obtained). It is possible that somefurther refinements and modifications tothe elements or layout may be required.Fact Sheet Three - Water Sensitive Urban Design Page 3 of 9

3 sustainable residential subdivision design fact sheet seriesThe District Council of Mount BarkerConstruction, operation andmaintenanceThe construction, operation andmaintenance phases must also be plannedand undertaken in a manner sympatheticto the natural environment. Thepreparation (as part of the developmentapplication) and effective implementationof a Soil Erosion and DrainageManagement Plan (SEDMP) is critical (andrequired by legislation) because it isduring the construction phase that theenvironment is normally placed at greatestrisk.Swales serve a number of functionsincluding:• removing sediments by filtrationthrough the vegetated surface• reducing runoff volumes (bypromoting some infiltration to the subsoils)• reducing erosion, as the vegetationstabilises the soil, and• delaying runoff peaks by reducing flowvelocities.It will also be important to ensure withCouncil that appropriate measures will beput in place for the ongoing operation andmaintenance of WSUD elementsincorporated on the development site.ComplianceIf Development Approval is granted, thedevelopment will be subject to conditions,which must be adhered to and areenforceable under the Development Act.WSUD OptionsAlternative WSUD options, when used inconjunction with conventional practices,have many cost, aesthetic andenvironmental benefits. Some of thesemeasures are detailed below.SwalesSwales are formed, vegetated depressionsthat are often used for the conveyance ofstormwater runoff from impervious areasas an alternative to the use of a kerb andgutter along roadways. They can also beused to convey stormwater flows inrecreational areas.The street crossfall can be designed to falltowards an adjacent swale on one side ofthe street or towards the median strip. Aswale may convey minor stormwaterflows, whilst the carriageway itself isdesigned to convey major stormwaterflows, as it would with a conventionalkerb, gutter and pipe system.Channel WorksEfforts should be made to retain thenatural alignment of any existingwatercourses through open space areas.Where it is necessary to increase channelcapacity, similar alignment and naturalshape should be maintained. Channelsshould be stabilised to avoid erosion,however, concreting of channels should beavoided. Stabilisation methods includeFact Sheet Three - Water Sensitive Urban Design Page 4 of 9

3 sustainable residential subdivision design fact sheet seriesThe District Council of Mount Barkeruse of vegetation, geofabric materials androcks.Sand / Gravel FiltersSand / gravel filters are a bed of sand orgravel overlying a subsoil drainagesystem. They can be used to remove oiland grit from stormwater runoff fromroads or car parks. These devices protectgroundwater and/or downstream surfacewater quality.soon as possible after rainfall andinundation. The standard of treatmentwill depend upon intended use.Detention BasinsDetention basins can be used to reducethe effect of increased peak flow ratesassociated with catchment urbanisation.They can either have a permanent waterstorage component (i.e. a wet detentionbasin) or are completely dry during nonfloodperiods (i.e. a dry detention basin).Both types can serve multiple objectives inaddition to their primary function of floodmitigation. Wet detention basins arecommonly utilised to provide waterpollution control, ecological andconservation functions as well as beingpublic passive recreational amenities. Drydetention basins often serve as playingfields and recreation parks in addition totheir flood mitigation function.Particular consideration is required tosurface and subsurface conditions withindry detention basins to ensure usability asAspects to consider in the design ofpermanent water bodies include:• quality of in-flowing waters and thestandard of recreation and amenitywhich can be supported• the need to incorporate grosspollutant traps or wetland filters• the range of habitats to be provided• the size and types of areas necessaryto fulfil various water quality and floodmitigation functions (i.e. sedimentbasin, shallow pools, large enough toprovide adequate detention time)• bank treatments to satisfy safetyrequirements, provide access andminimise erosion• requirements for boardwalks, jettiesand crossings to maximise use, andFact Sheet Three - Water Sensitive Urban Design Page 5 of 9

3 sustainable residential subdivision design fact sheet seriesThe District Council of Mount Barker• possibility of incorporating AquiferStorage and Recovery (ASR).Detention basins must be designed by aqualified civil engineer.Gross Pollutant Traps (GPTs) andSediment TrapsGPTs and sediment traps are utilised toreduce litter, debris and coarse sedimentsdischarging to receiving waters ordownstream treatment measures. Thelocation of GPTs should be chosen tomaximise the quantity of debrisintercepted and should focus on protectingreceiving waters but must be easilyaccessible for maintenance purposes.They can be installed in drain entrances,underground pipe systems, at pipe outfallsor on open channels.GPTs come in many forms and there arenumerous proprietary GPTs on the marketwhich fulfil different requirements.Therefore, if it is determined that a GPT isrequired, it is important to select theappropriate product to meet the specificneed of the particular development.Landscape MeasuresA wide variety of landscape measures canbe used to manage stormwater flows,utilise stormwater within the site andminimise supplementary watering oflandscaping. The careful design andplacement of landscape measures canhave many benefits in the water cycle,including reduced peak stormwaterdischarges, increased groundwaterrecharge, reduced erosion andsedimentation, increased retention of soilmoisture and lower watering costs. This isin addition to the likely water quality,aesthetic and ecological benefits.Examples of landscape measures includevegetated filter strips, contour banks,mulching and dense tree and shrubplanting.Street tree plantings should consider howleaf fall will affect stormwater drainageand aquatic ecosystems.Indigenous vegetation within allotments,streets and open space should beretained.Porous (or Permeable) PavingPorous paving is an alternative toconventional impermeable pavements withmany stormwater management benefits.These surfaces allow water to percolate toa sub-base course, from where itinfiltrates to the soil.A number of porous paving products arecommercially available including:• pavements made from special asphaltsthat allow stormwater to percolate toa sub-base course from where itinfiltrates to the soil• concrete grid pavements that allowstormwater to filter through voids inthe concrete, and• plastic modular block pavements thatallow stormwater to filter throughvoids in the plastic matrix.Benefits include reduced peak stormwaterdischarges, increased groundwaterrecharge, improved stormwater qualityand multiple-use of paved areas.Fact Sheet Three - Water Sensitive Urban Design Page 6 of 9

3 sustainable residential subdivision design fact sheet seriesThe District Council of Mount BarkerDesign and placement of porous pavingneeds to consider site conditions such asslope, soil conditions and traffic volumes.Construction costs of porous paving issimilar to that of traditional paving whensavings in stormwater infrastructure areconsidered.Rainwater Tank Collection / UseRainwater collected from roofs and storedin tanks is an excellent source of highquality water. Tanks can be designed notonly as a water source, but also to providetemporary stormwater detention. Benefitsof rainwater tanks include reduced mainswater demand, reduced water supplyinfrastructure costs, improvedenvironmental flows downstream of watersupply dams and reduced concentration ofstormflows in urban streams.New homes and household extensions ofgreater than 50m 2 are required to install arainwater plumbed for internal use whichmust have a capacity of at least 1,000 kL.Studies have demonstrated that a3,500 kL tank is able to supply water forindoor use 90% of the time in Mt Barker.Households within townships in theDistrict must also have 5,500 kL dedicatedfor firefighting (or 2,200 kL if householdsare located outside of the District).See Fact Sheet LG01 Rainwater Tank Use( Treatment / ReuseSystemThe majority of water used for indoordomestic purposes is discharged after useas ‘wastewater’. Wastewater is usuallycollected by a reticulated sewage systemand treated at a conventional wastewatertreatment plant. Alternatively it can becollected, treated and re-used on site. Ifon-site reuse of domestic wastewater isproposed there are various restrictionsthat need to be satisfied to ensure publichealth requirements and environmentalconcerns are met. Approval must beobtained from the Department of Health.See Draft Guidelines for Permanent OnsiteDomestic Greywater Systems:Greywater Products and Installation( further informationMaintenanceOnce established, multiple use of drainagesystems requires regular monitoring andpreventative maintenance to ensure thedrainage and water quality systemcomponents maintain their effectivenessand aesthetic appeal. Regularmaintenance is required to remove anyblockages and debris, repair erosion anditems damaged by floods and vandals, andto maintain vegetation and recreationsurfaces and facilities.The vast majority of potential problemsassociated with maintenance of WSUDelements can be eliminated by consideringmaintenance ramifications in the planningand design phase. It involves ensuringthat good design and constructionpractices are adopted.What tools are available tohelp me implement WSUD?A wide range of tools and resources areavailable to assist the implementation ofWSUD. Useful Websites substantial project is currently beingundertaken by Planning SA to provideguidance documents and similar webbasedresources in South Australia. In themean time, the use of the above web sitesis recommended.Fact Sheet Three - Water Sensitive Urban Design Page 7 of 9

3 sustainable residential subdivision design fact sheet seriesThe District Council of Mount BarkerTable 1: WSUD Principles and Legislative RequirementsWSUDPrincipleExample of WSUDApproachExample of ConventionalApproachLegislativeRequirementsProtectexistingnaturalfeatures andecologicalprocessesDisturbance to soils andlandscape minimised bymaintaining naturallandformsWaterways protected byproviding a buffer of naturalvegetation to urbandevelopmentNatural channel design andlandscaping used so thatthe drainage networkmimics the naturalecosystemVegetation completely clearedand landscape and waterwaysreshaped with major earthworksNatural waterways and drainagechannels highly modified andlined with concreteNatural waterways piped directlyto downstream waterwaysNative Vegetation Act1991Principle 21 DC MtBarker DPObjective 41 DC MtBarker DPObjective 49 DC MtBarker DPObjective 77 DC MtBarker DPMaintain thenaturalhydrologicbehaviour ofcatchmentsLimit the increase instormwater runoff volumeusing natural drainagepaths and infiltration basinsPiping and concrete lining of allwaterways and drainage lines toconnect stormwater runoff fromhard surfaces direct towaterwaysPrinciple 27 DC MtBarker DPPrinciple 46 DC MtBarker DPObjective 78 DC MtBarker DPObjective 79 DC MtBarker DPPrinciple 115 DC MtBarker DPPrinciple 204 DC MtBarker DPPrinciple 283 DC MtBarker DPProtect waterquality ofsurface andgroundwatersControl sediment-ladenrunoff from disturbed areasduring the constructionphase of the developmentAll stormwater runoff fromhard surfaces is treatedthrough infiltration,sedimentation, storage orbiological treatment beforeleaving the siteMinimal sediment and erosioncontrol measures duringconstructionStormwater directly dischargedto waterways without treatmentEnvironment ProtectionAct 1993 and theEnvironment Protection(Water Quality) Policy2003Objective 78 DC MtBarker DPPrinciple 169 DC MtBarker DPPrinciple 202 DC MtBarker DPPrinciple 304 DC MtBarker DPMinimisedemand onthereticulatedwater supplysystemRainwater tanks collect roofrunoff to supply toilet,laundry and outdoor usesHouses connected to (orutilise) a greywater orsewage recycling system toprovide an alternativesource of water for toiletflushing and outdoor useHouses incorporate waterefficient appliancesLow water use plants(preferably localprovenance) usedextensively in gardensTotal reliance on reticulatedsupply for all internal andexternal usesInefficient water appliancesLarge lawn areas and exoticplants in gardensObjective 83 DC MtBarker DPObjective 85 DC MtBarker DPObjective 87 DC MtBarker DPPrinciple 204 DC MtBarker DPBuilding Code ofAustralia (SA Provisions)Fact Sheet Three - Water Sensitive Urban Design Page 8 of 9

3 sustainable residential subdivision design fact sheet seriesThe District Council of Mount BarkerWSUD Example of WSUD Example of Conventional LegislativePrinciple Approach Approach RequirementsMinimisesewagedischarges tothe naturalenvironmentFit for purpose reuse isincorporated on-sitethrough recycling bathroomand laundry waterContribution to councilwastewater treatment andre-use schemeNo consideration given to waterreuse and recycling of sewageObjective 84 DC MtBarker DPIntegratewater intothe landscapeto enhancevisual, social,cultural andecologicalvaluesMinimise the use of hardengineered structuresNative vegetation is used instormwater managementand all landscaping tomaximise habitat valuesAll sewage treated at thesewage treatment plant anddischarged to waterwaysWater is ‘hidden’ in undergrounddrainage and pipe systemsObjective 49 DC MtBarker DPPrinciple 79 DC MtBarker DPPrinciple 116 DC MtBarker DPPrinciple 151 DC MtBarker DPPrinciple 283 DC MtBarker DPAdd valuewhileminimisingdevelopmentcostsReduces capital cost(pipework and drains)Community demand forenvironmentally sustainabledevelopmentDeveloper pays contribution fordownstream drainage capacitiesObjective 15 DC MtBarker DPThis Fact Sheet was produced byAustralian Water Environments Pty Ltdand Jensen Planning & Designwith funding assistance fromFact Sheet Three - Water Sensitive Urban Design Page 9 of 9

More magazines by this user
Similar magazines